The present invention relates to the field of fluid flows along a surface where there is significant diversion, and relates to air inlets of aircraft engines. The prior art includes in particular US Patent Application Publication No. 2008/156187 A1, EP Patent Application Publication No. 2009263 A2, FR Patent Application Publication No. 3023322 A1 and U.S. Pat. No. 5,447,283 A.
An air inlet duct of a turbine engine, in particular an aircraft turbine engine, is designed to guide air from the air inlet of the turbine engine to the gas generator. Some turbine engines, such as engines having unducted propellers, for example turboprop engines or engines of the type having a pair of contra-rotating propellers, can comprise an air inlet into the turbine engine having an axis different from that of the air inlet into the gas generator by which the propeller is driven. The axes thereof may be offset. This is generally the case for a turboprop engine where the axis of the propeller is itself offset with respect to that of the gas generator. This may also be the case at the front of an engine having a pair of contra-rotating propellers. FIG. 1 shows a turbine engine of this kind having two air inlets having axes which are offset with respect to that of the turbine engine. The air inlet shaft or duct therefore comprises a region in which the air flow is subject to significant diversion.
In this case, the air inlet duct comprises, between the air inlet and the gas generator, an intermediate cross-section having a relatively complex shape and, if applicable, a particle-removal channel forming a trap, which channel extends in the nacelle substantially along the axis of the air inlet and makes it possible to remove foreign bodies in order to prevent them from entering the gas generator.
When viewed from the side, the intermediate cross-section has the general shape of a gooseneck, the upstream end of which is connected to the air inlet in the nacelle and the downstream end of which is connected to the air inlet in the gas generator via a supply channel. The supply channel is positioned radially inwards with respect to the removal channel, and the intermediate cross-section comprises a part for connecting one channel to the other. There are other types of air inlet, each of these air inlets comprising a connecting part forming a diversion of the air flow.
The air inlet duct has the function of supplying the gas generator with air in the most homogenous manner possible. However, the above-mentioned complex shape of the pipe creates distortions in the air flow supplying the gas generator, which has a negative impact on the performance and operability of the turbine engine. This distortion is essentially due to the shedding of air streams caused by the significant diversion of the air flow in the above-mentioned intermediate cross-section.
One solution to this problem consists in incorporating vortex generators in the upstream end of the air inlet duct in order to energise the boundary layer and reduce the shedding. This could involve, for example, transposing passive devices which use vortex-generating means that are designed to control the shedding of air on the blades of turbine engines. FR 2 976 634, in the name of the present applicant, describes a device of this kind. Unfortunately it appears that, although this solution is practical, it would not be sufficiently effective in this type of design. Indeed, the duct opens very significantly in the diversion region and the disruptions required in order to limit the shedding of the boundary layer cannot be provided by a device of this type.
Another solution known from the prior art includes a system for actively controlling the shedding of the boundary layer in the air inlet ducts having significant diversions. For example, devices are known which suck air into the boundary layer of the flow circulating in the duct, which prevents the shedding of the flow, or which inject air at a very high speed in parallel with the wall so as to locally increase the amount of movement of the internal region of the boundary layer and to delay the shedding of the boundary layer and/or reduce the intensity thereof. Devices of this kind are complex and require elements for the circulation of air, by suction or blowing, to be installed in a compartment of the nacelle or close to the duct.
The aim of the present invention is to propose a system which makes it possible to reduce the flow shedding in the air inlet duct, in a targeted manner, and to thereby reduce the distortion in the region of the compressor while having as little impact as possible on operability and efficiency.